Sweethearting, in the realm of retail checkout systems, is the giving of unauthorized discounts or the abetting of shoplifting or other theft. Scan passing is a particular form of sweethearting where the cashier moves an item from the delivery belt to the bagging area without scanning the item with a barcode scanner (typically built into the checkout counter) so as to avoid the inclusion of the item in the customer's ring-up list of items to pay for.
A first technique for preventing fraud during retail checkout is scan gap detection, where longer-than-usual delays between successive UPC barcode scans are detected (based on the assumption that an efficient cashier scans items quickly at a fast and steady pace, and if scan passing fraud occurs, that rhythm is broken). Such technique generates too many false positives, thus requiring a high amount of time to review the exceptions thus generated.
A second technique is based on tracking items from belt to bag or bagging area. Such technique is unreliable, because it needs human presence in the loop to perform detections of fraud. Additionally, it is difficult to track all items without creating many mistakes.